Dart: a New Web Programming Experience

Once the onResponse() callback is executed, I pull the InputStream object
out of the response to begin reading data. I register the
onData(),
onClosed() and onError() callbacks to handle the different states the
InputStream can be in. onData() simply reads bytes off the stream and
appends them to the jsonData list object. onData() is guaranteed to be called as
long as there is data to read. Once the stream has hit "end of
file",
onClosed() is executed. At this point, I know all of the data from the
HttpRequest has been transferred and read, so I can use the JSON helper class
to parse the response into a Map object and print the final result to the user.
This is where the program actually exits from if everything was successful. If
there was an error in the InputStream, then the
onError() callback would have
been called, and the program would have exited from there.

To run this program, call it with the Dart runtime environment. You will need to
register for an API key from Weather Underground (http://www.wunderground.com/weather/api).
Don't worry; it's completely free. Once you have your API key, you can check the
current temperature for any US zip code:

Client-Side Dart

Now that you've seen what Dart can do on the server side, let's take a
look at what it really was designed for, the client side. Dart excels
at programming large-scale browser applications. Unfortunately, space
constraints prevent me from showing a truly large application.
Instead, I cover a not-so-large but very cool application using
the HTML5 Canvas object. Let's use Dart for finger painting.

In our simple finger-painting application, there will be buttons for each color
that is available to users, as well as buttons to increment and decrement the
thickness of their strokes. What good is painting a masterpiece if you can't
save it and share it with the world? So, let's make a save button that will
convert the canvas to a PNG image.

First, let's take a look at the markup for this project. In Listing 3, you
can see there is an HTML5 Web page that contains a canvas element called
draw-surface. This is where the work of art will be made. Below the
canvas are the control buttons that allow users to select colors and
stroke width, and the save button. The last part of the document is
the most interesting part. There are two script elements. The first is
a script tag with the type attribute set to "application/dart". This
script type is currently recognized only by a fork of Chromium called
Dartium (http://www.dartlang.org/dartium). The second is a JavaScript
bootstrap file that is required to start the Dart VM in Dartium. It also
has a special second function that I talk about later.

Now let's take a look at the application itself. At the top of Listing 2, I start
the program by importing dart:html. All client-side applications must import
this library to have access to the DOM. Next, I create a class called DrawSurface
that will act as a container class for the canvas object. The constructor takes
in a CanvasElement and grabs its 2-D-rendering context. It also registers all of
the callbacks to handle mouse movements on the draw surface. When the user
presses down on the mouse, somewhere on the draw surface canvas I begin a draw
path.

As the user moves the mouse around with the button pressed down, I add
line segments to the drawing. When the user releases the mouse or moves
out of the canvas element, I close the drawing path.

I implemented getters and setters for the color and lineThickness
attributes. In the setter methods, I make sure to update the rendering
context on any change. I also add two methods incrementLineThickness(int
amount) that will allow the user to adjust the lineThickness by some
amount, instead of just setting it, and
getPNGImageUrl() to expose the
canvas element's toDataUrl() method. This method will allow the save
button to function.

In main, I use the static query(String selector) function to get the canvas
element by its ID. The query function takes any CSS selector and returns
an Element object that matches it. If there is more than one element that
you want to access on a page, you can use the queryAll(String
selector) function
that will return a List<Element> object. I use this function to gather up all
of the color buttons at once and register onClick() events to set the current
color to its respective ID value.

Finally, I register the callbacks for the size-up and size-down buttons that
change the thickness of the line by 1. I also register the callback for the
save button to grab the PNG data URL from the canvas and open it in a new
window. The user then can save the image by right-clicking on it and choosing
"save image as".

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So when they found it hard to optimize Javascript some more they invented new language. Great, exactly like if college students write their own questions and answer them instead of teachers questions that are too hard to answer.

Things go away and things get backdated. JavaScript is no longer as great thing as past time. We used to invest prime time on this!

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As a computer scientist, I'm laughing. Google's Go and now Dart? Why don't you read between the lines of a $25 billion global corporation? Microsoft is a $50 billion global corporation. Today's Google == Evil news: "Google Abandons Open Standards for Instant Messaging". Yesterday, it was more evil news from Google. Wake up you clueless idiots!

privacy conscious users who want to use Off-the-Record encryption where possible, but to keep messages out of their Gmail accounts in any case, are out of luck. And if they wish to continue chatting with their friends on Google chat, they can't even take their business elsewhere.

provide Google with information about the content of their messages, or even when and from where they have logged in.

Comment: the google talk change, looks to be a mandate to compily with federal rules for tracablity.

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AFAICS the push to sophisticated browser-to-cloud applications will necessitate a shift from javascript. JS is great for a a bit of chunky screen animation and a bit of background I/O but I can't see that it is really up to running the big browser applications of the future. It's too messy in too many ways to develop something with a capacity like Photoshop. And this is where Google Docs etc are headed.

Dart is much more like CoffeeScript in the browser... It is a language, and an optional runtime is cross-compile to JavaScript, which is then run in the browser. The biggest wart is that debugging becomes very cumbersome and difficult. Other than that, I don't mind that it exists. There's also TypeScript if you're wanting an extension that cross-compiles to JS. For the record, I'm fine with JS, my style of programming tends to avoid a lot of the warts.

Moving away from class-based thinking, and more about module and functional patterns and passing state objects tends to work better anyhow. YMMV of course, but I happen to like JS as-is. That said, I don't fault anyone wanting to try something new/different.